Studies on meta effect appears in dioxetane chemiluminescence and ester photolysis

本文研究了间-和对-甲氧基苄基乙酸酯（I_m和I_p）在甲醇中的光分解，发现：（a）I_m的光化学C-O键断裂发生在激发单重态，而I_p的光化学C-O键断裂发生在三重态;（B）I_m光解的Φ_r明显低于I_p，这是由于紧密电子对的内部返回，即，C-O键裂变量子产额I_m为1，而I_p为0.8。C_m激发单重态的C-O键裂解非常容易，以至于光解产生单重自由基对和离子对起源产物，并伴有极低的荧光。由于C-O键在I_p激发单重态裂解缓慢，系统间跃迁成为激发单重态反应的主要途径，导致中等的荧光产率和高的三重态产率，并最终产生自由基源产物。决定I光解产物的主要因素是激发单重态中C-O键断裂与系间交叉的相对速率。本文用量子力学理论研究了I_m激发单重态C-O键断裂很快而I_p激发单重态C-O键断裂缓慢的原因，当3-甲氧基-3-甲氧基-（正-和对-甲氧基苯基）-4，4-金刚烷基-1，2-二氧杂环丁烷（II_m，II_p）在77 K下在玻璃态基质中光解，与甲氧基苯甲酸甲酯S_1态相邻的金刚烷酮作为外机，通过能量返回机制，使酯的电子自旋多重性由S_1变为T_1，酯和金刚烷酮之间的p-轨道重叠对于间甲氧基苯甲酸甲酯和金刚烷酮之间的能量返回机制起作用是必要的。在77 K下，II_p在玻璃态基质中光解生成的对乙氧基苯甲酸甲酯与金刚烷酮形成激基复合物。两个羰基片段之间的II_p断裂后立即发生的能量转移业务决定了半发光的命运。

Photolysis of m- and p-methoxybenzyl acetates (I_m and I_p) in methanol has been investigated and found the followings : (a) Photochemical C-O bond fission of I_m occurs from the excited singlet state, while that of I_p occurs from the triplet state ; (b) Φ_r apparently lower for I_m photolysis than for I_p is due to internal return of intimate pairs, I.e., the C-O bond fission quantum yield is 1 for I_m while 0.8 for I_p. c C-O bond cleavage of the excited singlet state of I_m occurs so readily that photolysis produce a singlet radical pair and ion pair origin products accompanied by extremely low fluorescence. Because C-O bonding splits slowly in the excited singlet state of I_p, intersystem crossing becomes the major pathway for excited singlet state reactions, resulting in a moderate yield of fluorescence and a high yield of the triplet state, and eventually yielding free radical origin products. The major factor determining I photolysis products is the relative rate of C-O bond cleavage in the excited singlet state versus intersystem crossing. The reason why C-O bond cleavage of excited singlet state of I_m is very fast while that of I_p is slow has been studied by quantum mechanical theory.When 3-methoxy-3-(w- and p-methoxyphenyl)-4,4-adamantiliden-l ,2-dioxetane (II_m, II_p) is photolyzed in a glassy matrix at 77K, adamantanone adjacent to S_l state of methyl methoxybenzoate plays as an external machine to alter electron spin multiplicity of the ester from S_l to T_l, by the energy return, mechanism, p-orbital overlapping between the ester and adamantanone is necessary to work the energy return mechanism between methyl m-methoxybenzoate and adamantanone. Intimate pair ofmethyl p-ethoxybenzoate and adamantanone generated through photolysis of II_p in glassy matrix at 77K forms exciplex. Energy transfer business that occurs immediately after the II_p fragmentation between two carbonyl fragments determines fate of ehemiluminescenee.